The Hidden Base

To gain access to the Secret Base mission, you will need to construct Alien Containment, and then capture and research both a Sectoid (or Thin man) and an Outsider. Doing so will reveal the location of a hidden alien base and allow you to to create the Skeleton Key necessary to unlock the entrance.

The Base Assault is your first serious command test. The narrow corridors channel you into nasty bottlenecks where waiting Chrysslids often attack out of nowhere. Every doorway into a larger antechamber is a sure sign of impending ambush. Drones also appear here, and you should dispatch them on sight to nullify their healing abilities.

Move even more cautiously than normal here. There is no time limit, so advance with purposeful, thoughtful pacing. You will encounter Drones, Floaters and Chryssalids, among other menaces.

When you reach the end of this mission you will encounter your first Sectoid Commander. His Mind Control ability has a very long range and can tear your squad apart by turning allies into enemies. Mind Control only breaks after three rounds have passed or the Commander is killed. Waiting the Control out is rarely an option. A compromised friendly unit usually has the benefit of already flanking you. The most reliable tactic against this single Commander is therefore an all-out attack concentrating your entire squad’s fire, even if this means breaking cover.